"I can't give up either humanity or freedom," Joseph Roth announced in a 1935 letter to fellow Austrian novelist Stefan Zweig. Freedom was the right to fit all his possessions into two suitcases and to live in hotels; to move in a single year from Austria to Germany to France to Russia; to have no address and no bank account. He was married, to a woman committed to a mental asylum, and he had a long-term mistress. But he avoided "cooking smells and 'family life'". "I shit on furniture. I hate houses." He nevertheless felt a duty to support these women, along with their parents and children. Roth was often penniless but he still shared what money he had with eight others.

On a wider scale, freedom was the license to spurn friends or nations lacking in humanity. Roth was living in Germany in 1933, but the day that Hitler became chancellor he left and never returned. "What divides me from everyone, without a single exception, who is active in Germany," he told the more accommodating Zweig, "is precisely what divides a human from an animal".

Living this uncompromisingly was exhausting and expensive. By 1935 Roth had borrowed money from every friend, publisher and waiter who was prepared to lend it. He worked for 10 hours a day, producing daily articles and yearly novels, but was a bad businessman and an inveterate alcoholic, whom Zweig admonished for spending more on drink than the average family spent on living (Zweig himself was living on considerably more than that, of course). As a result, Roth was physically disintegrating. He was vomiting spleen and blood; his eyes were inflamed and his feet swollen; he was losing his hair and his teeth.

This is the Roth who spews and shouts from his letters, now made available in English for the first time by Michael Hofmann. There is no biography of Roth in English, so for many readers this will be the first glimpse of the man behind the novels. Readers of The Radetzky March will be able to identify Roth with aspects of his most famous character, Lieutenant Trotta, who is also a wandering, self-destructive alcoholic. But where Trotta responds passively to events, his creator hurled himself at the world, energetically railing against it even as he lost the battle for his own survival. In one of the excellent biographical essays that punctuate this volume, Hofmann characterises Roth as "a man going over the edge of the world in a barrel". Roth knew that he was doomed, but he propelled himself along, wreaking destruction as he went, often through the letters and telegrams that he penned frantically and posted urgently ("pretend the telegram has been disinvented," Zweig once pleaded).

These letters prove the ideal medium to get to know a man who resisted conventional biography, occluding his own life in myth. In Wandering Jew, a fascinating exploration of Roth's Galacian origins, Dennis Marks describes Roth as "one of literature's most prodigious liars". Roth continually reinvented his birthplace and early history, and often contradicted himself. His letters, unfolding over time, enable these contradictions and alternative stories to coexist. He can tell the younger writer Bernard von Brentano that the experience of love is delusory, evaporating after sex, "just as pink elephants go away when you have a drink", only to fall in love himself and insist that love alone can enable him to feel alive. He can assure Brentano that he will "always be your friend", only to announce four years later that Brentano is one of the few people he would happily murder "with no more compunction than putting out a cigarette".

Yet some views remain consistent in the letters, and Roth emerges as an idiosyncratic conscience for his age. Throughout, he hates Germany, with its fake elegance, loud voices and ugly prostitutes, and more dangerously its nationalist leanings. And his loathing of nationalism leads him to despise Zionist Israel almost as much as he reviles anti-semitic Germany. "A Zionist," he says controversially, "is a National Socialist, a National Socialist is a Zionist." His own Jewishness he describes as "a metaphysical affair". Though happy to define himself as a Jew, he was spiritually a Catholic.

This is an odd collection, in that there are no letters to Roth's wife or mistresses, and very few to his family. The descriptions of his romantic affairs are less frequent than the lists of his mounting debts. But it becomes clear that his passion lay more in literature and friendship than in love and marriage. In this respect the letters do enable us to access Roth's most fervent and personal side, most of all through the correspondence with Zweig. Roth's friendship with him was typically formal. In 1930 Zweig persuaded Roth to drop the "Mr" but Roth still refrained from addressing Zweig as "Stefan". However the formality did not prevent the expression of passionate love and hate. Roth was fiercely loyal to "the umbilical cord of friendship" with Zweig but often threatened to end the friendship if Zweig failed to distance himself sufficiently from Germany. "I will cease to love you the moment you become a child of the world."

In the end, Roth did abandon Zweig. There are very few letters to him in the year before Roth's death in May 1939. Hofmann, whose own antagonism to Zweig is well-known, clearly applauds Roth's recognition of his own superiority both as a writer and a man. In one of the dogmatic footnotes that help to make this volume entertaining, Hofmann tells us that Roth is the better writer and any English readers who conflate them are "basically illiterate and unpardonable". And certainly, Roth materialises as a greater man here. He was a failure in worldly terms; he was maddening as a husband, colleague and friend. But he was prescient and uncompromising and he lived on an impressively huge scale, sacrificing dignity for the sake of honesty and fervour. "I have no home, aside from being at home in myself," he wrote in 1930. "Wherever I am unhappy is my home." Roth emerges in the letters as the tragic hero that he refused in his fiction.